118 VETERINARY PATHOLOGY. 



oede:\ia, dropsy or hydrops. 



DEFINITION. 

 ETIOLOGY.- 



Increased production. 



Increased pcrnieabilily {Colinheiin.) 



Increased pressure. 

 OBSTRUCTED OUTFLOW. 



Valvular insufficiency or stenosis (cardiac). 



Gravid uterus. 



Tumor, Abscess, Ligature, etc. 

 LOCATION. 



Peritoneal cavity (ascites). 



Thoracic caz'ity (hydrothorax) . 



Pericardial caz'ity (hydro pericardium). 



Arachnoid space {liydrocephalus external). 



Lateral vottricles (hydrocephalus internal). 



Tunica c'oginalis cavity (hydrocele) . 



Subcutaneous lymph spaces (anasarca) (in legs onlv, stocking). 

 APPEARANCE. 



Macroscopic. 



Microscopic. 

 EFFECTS. 



Oedema, dropsy or hydrops is the accumulation and retention 

 of lymph in the lymph vessels and spaces. Lymph is the 

 conveyor of metabolic substances to and from all tissues of 

 the body except those directly supplied by the blood capillaries. 

 The quantitv of lymph in the lymphatic channels is determined 

 by the permeability of the capillary walls and the rapidit_v of 

 lymphatic al^sorption. In health there is a balance between 

 the transudation of lymph from the blood vessels and its 

 absorption into the lymph vessels. In oedema there is either 

 a lar_8;-er amount of lymph transuded or a smaller amount 

 absorbed. 



Etiology. — The causes of oedema may be : 



1. IiicrAiscd transudation which may be caused by (A) 

 Increased permeability (or secretory function) of the capillary 

 walls, thus allowing- an increased amount of fluid to escape 

 from the blood. (V>) II}'])eremia : which produces an in- 

 creased intracapillary pressure resulting in sufficient injury 

 to the endothelial lining to allow an increased outflow of 

 plasma. Passi\'e hyperemia is more frequently associated with 

 oedema than active hyperemia. Thus, tricuspid stenosis or 

 tricuspid insufficiency is usually associated with general dropsv. 

 "Stocking" is an oedema usually resulting from venous hyper- 

 emia. 



2. Obstructed outfloza of lymph. Swollen lymphatic glands, 

 the result of inflammatory disturbances or neoplasms, and 



